label and goto Statement

goto statement:
goto statement transfers control from one part of the program to another.  It is an unconditional jump(control transfer) statement.  Below is the syntax for goto statement.

Syntax:
goto label;
.......
label:

We have to specify label for goto statement.  When goto statement is executed, program control transfers to label.

What is a label?
Label is just an identifier followed by a colon.  Label is usually associated with goto statements and it used to identify where the control needs to be transferred while executing goto statement.

goto err;
.....
err:   // err is a label

Note:
Label name needs to be an unique identifier and there should be at least one statement next to label.

Example C program using goto and label:

 
   #include <stdio.h>
   int main() {
           int input, i, data[100], count;
           printf("Enter Positive integers alone as input:\n");
           for (i = 0; i < 100; i++) {
                   scanf("%d", &input);
                   if (input < 0)
                           goto err;

                   data[i] = input;
          }
          printf("All your inputs are positive values\n");
  err:
          count = i;
          printf("Outputs:\n");
          for (i = 0; i < count; i++)
                  printf("%d\n", data[i]);
          return 0;
  }

  Output:

  jp@jp-VirtualBox:~/$ ./a.out
  Enter Positive integers alone as input:
  1
  2
  3
  4
  -5
  Outputs:
  1
  2
  3

  4

Here the user has given -5 as his 5th input.  Since it is a negative integer value, goto statement is executed which in turn transfers program flow to the section of code below the label err.

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